A prosthesis (10, 300) is provided for implantation at a native semilunar valve (140, 310) of a native valve complex. The prosthesis (10, 300) includes a distal fixation member (14), configured to be positioned in a downstream artery (160, 314), and shaped so as to define exactly three proximal engagement arms (22) that are configured to be positioned at least partially within respective ones of semilunar sinuses (164), and, in combination, to apply, to tissue that defines the semilunar sinuses (164), a first axial force directed toward a ventricle. The prosthesis (10, 300) further includes a proximal fixation member (12) coupled to the distal fixation member (14), the proximal fixation member (12) configured to be positioned at least partially on a ventricular side of the native semilunar valve (140, 310), and to apply, to the ventricular side of the native valve complex, a second axial force directed toward the downstream artery (160, 314), such that application of the first and second forces couples the prosthesis (10, 300) to the native valve complex.
